Multiconductor transmission media

ABSTRACT

In order to reduce the undesirable electrical effects of insulation which is inherently eccentrically applied to individual conductors, on the spacing between conductors when they are stranded into a multiconductor communications wire or cable, the inherent eccentricity of the insulation on each of the individual conductors is distributed spirally about the axes of the individual conductors in different patterns so that the occurrences of periodic matching of eccentricity of the insulation on the adjacent stranded conductors of the wire or cable is reduced and the spacing between the conductors is more nearly equalized, thereby reducing the electrical unbalance and resultant electrical effect commonly known as &#39;&#39;&#39;&#39;crosstalk&#39;&#39;&#39;&#39;.

United States Patent [72] Inventors William P. Brauns Severna Park; George E. Hartranl't, Parkville, both of,

[54] MULTICONDUCTOR TRANSMISSION MEDIA 5 Claims, 9 Drawing Figs.

[52] U.S. Cl 174/34, 174/113 [51] IIILCI ..HOIb 11/06 [50] Field of Search 174/32, 33, 34, 113

Primary Examiner-E. A. Goldberg Attorneys-R. P. Miller, Don P. Bush and W. M. Kain ABSTRACT: In order to reduce the undesirable electrical effects of insulation which is inherently eccentrically applied to individual conductors, on the spacing between conductors when they are stranded into a multiconductor communications wire or cable, the inherent eccentricity of the insulation on each of the individual conductors is distributed spirally about the axes of the individual conductors in different patterns so that the occurrences of periodic matching of eccentricity of the insulation on the adjacent stranded conductors of the wire or cable is reduced and the spacing between the conductors is more nearly equalized, thereby reducing the electrical unbalance and resultant electrical effect commonly known as crosstalk.

MULTICONDUCTOR TRANSMISSION MEDIA This is a division of application Ser. No. 638,488, filed May 15, I967 now U.S. Pat. No. 3,487,540 issued Jan. 6, 1970.

BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates to plural conductor wires or cables in which inherently eccentrically applied insulation on individual conductors is disposed spirally about the axes of the individual conductors in different predetermined patterns to improve the electrical properties of the wire or cable.

2. Description of the Prior Art ln telephone installations, an increasing amount of use is being made of multiservice handsets which require more than a single pair of conductors to connect the handsets to a terminal point. Residence-type telephone handsets with services such as lighted dials are connected with four-conductor station wires. Also, in commercial and industrial installations, central terminal points are connected to handsets with station wires and very often it is convenient to use four-conductor station wires. Because a majority of station wires installed today are used in applications like the ones described above, and because it is economical to reduce the number of types of station wires used, craftsmen installing telephone systems have begun the practice of installing four-conductor station wires in many applications where two or three-conductor wires would ordinarily suffice. The substantial use of four-conductor station wire has created an atmosphere where improvements in quality and cost of four-conductor station wires can be very profitably pursued. Some improvements to four-conductor station wires are described in a pending application, Ser. No. 613,188, filed on Feb. 1, 1967, in the names of N. J. Cogelia, S. M. Martin and R. B. Ramsey.

The use of four-conductor wires leads to situations where two talking circuits are handled on the same station wire; and in the case of telephone sets with lighted dials, a talking circuit and a 60-cycle lighting circuit are contained in the same station wire. The use of two talking circuits or one talking circuit and a 60-cycle lighting circuit in close proximity gives rise to a well-known problem of the telephone industry known as crosstalk. Crosstalk develops when a first circuit induces a disturbing signal in conductors of nearby circuits, which, of course, become disturbed circuits. An induced signal in the disturbed pair occurs when the electric or magnetic fields generated by one of the conductors of the disturbing pair creates a current in one of the conductors of the disturbed pair, and this induced current is not precisely opposed by an induced current in the other conductor of the disturbed pair. The net induced current so obtained is heard by the telephone subscriber as crosstalk or noise.

One way of eliminating or at least significantly reducing the net induced currents in a imaginary station wire is to place the conductors in a star quad configuration, wherein the four conductors of two paired circuits are placed in the corners of an imaginary square; and diagonally disposed conductors are used as the components of paired circuits. When the spacing between conductors of a star quad is exactly equal and the dielectric material therebetween is distributed uniformly, the currents induced in the two conductors of the disturbed pair will be equal and opposite, thus a state of electrical balance is more nearly achieved. Any inequality in spacing contributes to creating electrical unbalance.

A star quad structure is commonly used in station wire today. Previously designed star quads were adequate to create satisfactorily electrically balanced circuits over short distances. In more recent times, as longer and longer distances are required to be spanned by such station wires, cross splices were made in the station wire at intervals of approximately 100 feet in order to help attain electrical balance. The cross splicing of such wires is obviously time consuming and expensive; and in some cases, lengths of over 100 feet were required in locations not readily accessible for splicing.

In order to overcome these difficulties, it was desirable to provide for more uniform spacing between conductors in order that longer lengths of station wire could be used without cross splicing. However, obvious limitations existed with respect to methods and apparatus with which the uniform spacing could be accomplished economically. One of these limitations related to the methods and apparatus used for forming plastic insulation on the individual conductors of the station wire. The plastic insulation of each conductor of a station wire is applied separately by an extrusion operation. Due to the characteristics of particular extruders, the insulation applied to any conductor is often eccentric to a certain extent. In other words, no matter how well the extruder is adjusted, the insulation will probably be thicker on one side of the wire than on the other. This almost inevitable eccentricity results in unequal spacing between insulated conductors and consequently the mutual capacitance of the different pairs of conductors will vary and other electrical unbalances will develop when the insulated conductors are formed into multiconductor wires or cables such as star quads.

The effect of this eccentricity of insulation has been found to be reduced when the insulated conductors are pretwisted about their own axes before they are stranded together into a quad or other multiconductor configuration. Pretwisting distributes the eccentricity of insulation into a helical pattern along the insulated conductor; and when the insulated conductors are placed adjacent to each other, they appear to be more nearly electrically equally spaced and less unbalance exists.

Simple pretwisting can achieve good electrical balance for conductors where the eccentricity is minimal; however, in most commercially manufactured wire, it is difficult and often uneconomical to provide minimal eccentricity. On the other hand, eccentricity may often be quite severe. ln these case, it is important to provide a pretwisting pattern which will not allow the thin and thick areas of adjacent conductors to come in contact with any regularity or periodicity.

While it is important to control electrical unbalance, it is still a prime consideration in manufacturing station wire to make the wire at as low a cost as possible. In the past, the pretwisting of insulated conductors of station wire has added considerably to the cost of station wire because reels of wire had to be specially handled and often separate operations were required to be performed on the wires to accomplish the pretwisting.

SUMMARY OF THE INVENTION lt is an object of the present invention to provide multiconductor electrical transmission media having improved electrical characteristics.

lt is a further object of the present invention to provide multiconductor electrical transmission media having improved electrical balance between conductors in circuits of the media in order to control the effect of currents which adjacent circuits introduce in each other by having the insulation on the individual conductors positioned about the axes of the individual conductors in such a way that the probability of periodic or regular matching of inherent eccentricity of the insulation on the conductors is reduced.

It is another object of the invention to improve the electrical balance between conductors in circuits of a communication wire or cable in order to control the effect of currents which the circuits induce on each other and to accomplish this control of electrical balance by having inherent eccentricity of the insulation of adjacent individual conductors disposed spirally of their own axes in predetermined different patterns so that the probability of periodic or regular matching of eccentricity of insulated conductors is reduced.

A manufactured product illustrating certain features of the present invention may include a multiconductor electrical transmission medium, which includes a plurality on insulated conductors having insulation applied thereto eccentrically of the conductive cores thereof, with the eccentricity of the eccentrically applied insulation with respect to the individual cores of at least two adjacent insulated conductors in the transmission media being disposed spirally with different patterns of spiral disposition.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and features of the present invention will be 'more readily understood from the following detailed description of specified embodiments thereof when read in conjunction with accompanying drawings, in which;

FIGS. 1A, B and C depict sectional views through a stranded and jacketed wire product of the prior art in which individual insulated conductors are not twisted about their own axes; the views being taken at various lengths along the stranded wire product and the distances between FIGS. 1A, 1B and 1C being even multiples of the stranding lay length of the stranded wire product;

FIGS. 2A, B and C depict sectional views through a stranded wire product of the prior art in which the individual insulated conductors are twisted about their own axes with an equal twist length; the views being taken at various lengths along the stranded wire product so that the distance between FIG. 2A and FIG. 2B is an even multiple of the stranding lay length and a half multiple of the twist length of the insulated conductors, and the distance between FIGS. 2A and 2C is an even multiple of the stranding lay length and an even multiple of the twist length of the insulated conductors, and

FIGS. 3A, B and C depict sectional views through the stranded wire product embodying certain principles of the present invention in which each of the individual insulated conductors is twisted about its own axis with a different length of twist; the views being taken at various lengths along the stranded wire product so that the distance between FIGS. 3A, 3B and 3C is an even multiple of the stranding lay length; but, because of the unique twist imparted to each of the insulated conductors, the distance is not a multiple of the length of twist of the insulated conductors.

DETAILED DESCRIPTION Referring now to the drawings, there are shown sections through a jacketed, stranded wire product, designated generally by the numeral 16, in which an extruded jacket thereof is illustrated in phantom for purposes of simplicity. The jacket 15 is extruded in the manner described in a pending application, Ser. No. 613,188, filed on Feb. I, 1967 in the names of N. J. Cogelia, S. M. Martin and R. B. Ramsey. Insulated conductors, designated generally by the numerals 18-18, are arranged in a formation which is often referred to as a star quad.

In all of the sectional views, each of the insulated conductors 18-18 includes a conductive core 22 and an insulating coating 24 applied eccentrically thereon. The insulating coating 24 of each of the insulated conductors 18-18 is a different color. The colors used in the illustration are black, green, yellow and red and are typical of those used in the telephone industry on station wire.

Looking now to the configuration in which the insulated conductors 18-18 are nontwisted as shown in FIGS. 1A, B and C, one can see that the spacing between the conductive cores 22-22 of the yellow insulated conductor and the red insulated conductor is different from the spacing between the conductive cores of the green insulated conductor and the red insulated conductor. The red and green insulated conductors 18-18 are components of one paired circuit and the black and yellow insulated conductors are components of another paired circuit within the stranded wire product 16.

When none of the insulated conductors 18-18 are twisted about their own axes, it can be seen that a constant inequality in spacing can exist throughout the length of the stranded wire produce 16. Even though successive portions of each of the insulated conductors 18-18 change their orientation with respect to general space along the length of the stranded wire produce 16, the orientation ofany of the insulated conductors within the stranded wire product does not change with respect to any of the other insulated conductors within the stranded wire product. Due to the fact that there can develop a constant inequality in the spacing between the conductive cores 22-22 of a disturbed and a disturbing pair in the untwisted configuration, there is a high probability that crosstalk and noise will develop because of the ensuing electrical unbalance caused by the inequality in spacing.

Looking now to FIGS. 2A, B and C, one can see'that some improvement over the untwisted configuration can be obtained by twisting each of the insulated conductors 18-18 about its own axis. FIG. 2A, again shows conductive cores 22-22 on which eccentric insulativc coatings 24-24 have been applied. Again, there may develop an inequality in spacing between the conductive cores 22-22 of a disturbed and a disturbing pair, but FIG. 2B shows that when the insulated conductors 18-18 are twisted about their own axes their orientation with respect to each other may change as well as their orientation with respect to general space. In other words, the inequality in the spacing between the green and yellow conductors 18-18 and the red and yellow conductors as shown in FIG. 2B is not necessarily the same as it was in FIG. 2A, and it can be readily seen that this changing of orientation of insulated conductors 18-18 with respect to each other produces statistically a situation wherein the subject spaces approach electrical equality.

FIG. 2C shows a point which is one twist pitch length of the insulated conductors 18-18 away from FIG. 2A. It can be seen by comparing FIGS. 2C and 2A that the orientation of the insulated conductors 18-18 with respect to each other will probably be the same; and, therefore, the inequality in spacing will probably be the same. Thus, there may very well exist a situation where an inequality in spacing occurs on a repetitive or periodic basis; and this recurring inequality in spacing would be likely to adversely effect the statistical electrical equalization of spacing between the conductive cores 22-22 achieved by pretwisting.

However, in accordance with the present invention, this condition can be improved if the twist lengths of all four insulated conductors 18-18 are not the same. In FIGS. 3A, 3B and 3C, there is illustrated a case in which all four of the insulated conductors 18-18 have been twisted about their own axes with different twist lengths. FIGS. 3A, 3B and 3C all show unique spacings of the conductive cores 22-22. In this case, it is improbable statistically that a situation where repetitive inequalities in spacing will occur; and, therefore, statistically, the probability for eliminating electrical unbalance is extremely high.

The foregoing discussion has pointed out the advantages of the improved twisting technique on the reduction of crosstalk and noise in a stranded wire product 16. It is also important to note that the equalization of spacing between the conductive cores 22-22, which develops statistically, is advantageous to control uniformity in the capacitance which develops between the conductive cores of any particular paired circuit. This controlling of uniformity in capacitance in a paired circuit has a direct effect on the control of impedance of that circuit and, consequently, its efficiency in transmitting high frequency signals.

In cases where the stranded wire product 16 might be enclosed in a grounded shield (not shown), the capacitance which would develop between the conductive cores 22-22 and the shield should be kept uniform in order to make the electrical interaction between conductive cores and the shield predictable. The unmatched twisting of the insulated conductors 18-18 would help equalize the spacing which would develop between the conductive cores 22-22 and the shield (not shown) and would thus contribute to uniformity of capacitance. The level of noise or crosstalk induced into the conductive cores 22-22 of a paired circuit by the shield would be made minimal when the capacitance between these elements became uniform.

Predictability of the capacitance which will develop between two of the conductive cores 22-22 used as a paired circuit or between one of the conductive cores and the shield (not shown) which might be used is important because station apparatus can be better designed when parameters such as the subject capacitances can be relied upon by a designer to have definite values.

An example of a specific embodiment of the stranded wire product 16 and the one illustrated in FIGS. 3A, B and C is a star-quadded telephone station wire in which the stranding lay is 4 inches and the individual insulated conductors 18-18 are twisted about their own axes with pitches of 38 inches, 4l inches, 45 inches and 48 inches, respectively.

What we claim is:

l. A plural conductor electrical transmission medium having improved electrical characteristics, which comprises a plurality ofindividually insulated conductors, each insulated conductor including a conductive core and an insulating material surrounding at least a portion of the core, the insulating material on each conductor having some degree of eccentricity with respect to the associated conductive core, and the eccentricity of the insulating material of at least two adjacent conductors being disposed spirally about their associated conductive cores, the pattern of spiral disposition of the eccentricity of the insulating material along a substantial length of the transmission medium of one of the conductors being different from the pattern of spiral disposition of the eccentricity of the insulating material of at least one of the adjacent insulated conductors in the transmission medium.

2. The plural conductor transmission medium of claim 1, wherein the insulated conductors having spirally disposed insulating material are twisted about their own axes with different lengths of twist so that the pitches of the spirally disposed insulating material of adjacent sections of adjacent conductors are different.

3. The plural conductor transmission medium of claim 2, having a star quad in which all of the four conductors of the quad are twisted about their individual axes with different lengths of twist.

4. The plural conductor transmission medium of claim 3, wherein the conductors of the quad are disposed spirally with respect to the longitudinal axis of the quad with a lay substantially shorter in length than the pitches with which the insulated conductors are twisted about their individual axes.

5. A plural conductor electrical transmission medium having improved electrical characteristics, which comprises a plu' rality ofindividually insulated conductors, each insulated conductor including a conductive core and an insulating material surrounding at least a portion of the core, the insulating material on each conductor having some degree of eccentricity with respect to the associated conductive core, and the eccentricity of the insulating material of at least two adjacent conductors being disposed spirally about their associated conductive cores, the pattern of spiral disposition of the eccentricity of the insulating material along a substantial length of the transmission medium of at least one of the conductors being in a predetermined spiral pattern different from the pattern of spiral disposition of the eccentricity of the insulating material of at least one of the adjacent insulated conductors in the transmission medium, 

1. A plural conductor electrical transmission medium having improved electrical characteristics, which comprises a plurality of individually insulated conductors, each insulated conductor including a conductive core and an insulating material surrounding at least a portion of the core, the insulating material on each conductor having some degree of eccentricity with respect to the associated conductive core, and the eccentricity of the insulating material of at least two adjacent conductors being disposed spirally about their associated conductive cores, the pattern of spiral disposition of the eccentricity of the insulating material along a substantial length of the transmission medium of one of the conductors being different from the pattern of spiral disposition of the eccentricity of the insulating material of at least one of the adjacent insulated conductors in the transmission medium.
 2. The plural conductor transmission medium of claim 1, wherein the insulated conductors having spirally disposed insulating material are twisted about their own axes with different lengths of twist so that the pitches of the spirally disposed insulating material of adjacent sections of adjacent conductors are different.
 3. The plural conductor transmission medium of claim 2, having a star quad in which all of the four conductors of the quad are twisted about their individual axes with different lengths of twist.
 4. The plural conductor transmission medium of claim 3, wherein the conductors of the quad are disposed spirally with respect to the longitudinal axis of the quad with a lay substantially shorter in length than the pitches with which the insulated conductors are twisted about their individual axes.
 5. A plural conductor electrical transmission medium having improved electrical characteristics, which comprises a plurality of individually insulated conductors, each insulated conductor including a conductive core and an insulating material surrounding at least a portion of the core, the insulating material on each conductor having some degree of eccentricity with respect to the associated conductive core, and the eccentricity of the insulating material of at least two adjacent conductors being disposed spirally about their associated conductive cores, the pattern of spiral disposition of the eccentricity of the insulating material along a substantial length of the transmission medium of at least one of the conductors being in a predetermined spiral pattern different from the pattern of spiral disposition of the eccentricity of the insulating material of at least one of the adjacent insulated conductors in the transmission medium. 